The present invention relates in general to a mark position detecting method and its apparatus. In particular, the present invention relates to a method of detecting a center position of a positioning reference mark formed on a mask for a pattern transfer by an energy beam, which is used for a mask defect inspection system, and an apparatus for executing the mark position detecting method.
In manufacturing the semiconductor integrated circuit (IC) chips, a reference pattern is formed on a mask for transferring a given micro-circuit pattern on a specimen. If the reference pattern contains a pattern defect such as disconnection, a manufacturing yield is reduced. To cope with this problem, a mask defect inspection system for inspecting a pattern defect prior to manufacturing the integrated circuits, has been developed. In this system, a mask member is illuminated to produce an optical signal representing a micro-circuit pattern formed on the mask member. This optical signal is compared with a theoretical data signal obtained on the basis of the design data used for forming the mask pattern. The optical signal representing a defect-contained mask pattern is not coincident with the theoretical data signal. The mask defect inspecting system detects the result of the comparison and judges whether or not a defect is present in the mask pattern.
For inspecting a pattern defect by using the mask defect inspecting system, it is essential to exactly align an optical system in this inspection system with the mask member in a high accuracy. An insufficient accuracy in the alignment between the optical system and the photomask results in an inaccuracy of the mask defect inspection. At the present stage, it is difficult to effectively and automatically detect the coordinates of a center position of a small positioning reference pattern previously formed on the mask.